1. Field of the Invention
The present invention relates to a vehicular alternating current generator (i.e., alternator), and in particular, to a brushless type of alternating current generator mounted in motortrucks, construction machines, agricultural machines, and others.
2. Description of the Related Art
In recent years, manufactures for passenger automobiles and motortrucks have been improving the engines so as to comply emission standards. This improvement tends to increase the ambient temperature around the components mounted on an engine. Also, safety devices, additional power supplies, and other in-vehicle amenities have increased gradually, whereby electrical loads to an alternating current (AC) generator (alternator) in each vehicle are on the increase.
The vehicular AC generator can be divided into two types in terms of its brush structure. One type is an AC generator with brushes, which are mainly for passenger automobiles. The other type is known as a brushless type of AC generator, which is generally longer operating line. This generator is mainly for motortrucks which travel for a long time, and construction and agricultural machines obliged to work in adverse environments with dust. The brushless type of AC generator is disclosed by Japanese Patent Laid-open Publication No. 2002-95215.
In the brushless type of AC generator disclosed by the publication, there is a housing which encloses various components. However, the housing has no cooling windows formed through its side walls, because the existence of the cooling windows may allow inhalation of foreign materials and liquid from the outside and also physical damage from the outside. This may result in short-circuited or damaged electrical parts. In addition, the electrical parts such as a rectifier are generally protected by the housing side walls. Cooling for such electrical parts is realized by external cooling fans screwed to the rotary shaft of the generator.
Recent needs for the AC generator involve making it compact in size and raising its output. Such needs are met by enlarging the outer diameter of a stator mounted in the generator, elongating the stack thickness of the stator, and/or reducing the resistance of windings wound in the stator. However, there still remains a problem that the higher output causes the internal electric parts to have higher temperature.
Of course, one known countermeasure is to increase the mount and/or speed of air blown by the cooling fans. However, the external fans provided in the brushless type of AC generator is impossible to increase their outer diameters, due to a limitation in fan size along the radial direction.
Another countermeasure is to increase the number of fan blades and/or the axial area of the fan blades. However, this measure may decrease the strength of the fan blades, which therefore limits the increase in the number and/or area of fan blades. This makes it difficult to obtain a desired speed and/or amount of cooling air.
Still another countermeasure is to narrow the gap between radiating fins of electric parts, such as the rectifier, and side walls of the housing so that the cooling air is allowed to sufficiently pass around the radiating fins and through the inside of the housing. However, this narrowed-gap technique tends to cause foreign matters to be accumulated in the gap, because of a reduction in the creeping distance (i.e., clearance or insulating gap) therebetween. The accumulated foreign matters may cause an electrical short circuit, reducing operational reliability of the generator.